1. Field of the Invention
The present invention is related to a photo-sensing circuit used in a camera, etc., particularly to a photosensing circuit employing a photo-electromotive element.
2. Description of the Prior Art
Recently, photoelectromotive elements such as a selenium photocell, a silicon photo-cell, etc. are used as a light receiving element of the photo-sensing circuit of a camera.
Said photo-electromotive element has the shortcoming that its linear output characteristic range becomes narrow because of the load resistance connected to said element. Otherwise it has various good characteristics, such as small temperature variation, small changes due to aging, etc.
Thus a device having an element with the resistance value of the load resistance connected thereto being made virtually zero, eliminating the above mentioned shortcoming of the conventional device, was disclosed in British Pat. No. 1,293,771.
But, the circuit in other a device has such shortcomings the that its function becomes unstable because of the variation in ambient temperature as the resistance value of the load resistance is almost zero, and that since the load resistance of the photo-electromotive element is made almost zero, a computation amplifier is used. Accordingly the system of the device becomes complicated and costs high.
An object of the present invention is to provide a photo-sensing circuit in which the above mentioned shortcomings of conventional devices are eliminated.
Another object of the present invention is to provide a photo-sensing circuit in which a photo-conductive element is used as the load resistance of the photo-electromotive element.